The present invention relates generally to printing devices and, in some embodiments, to methods and systems for allowing for accurate indexing of print receiving media in such printing devices.
In printing devices, a media indexing system advances or indexes the media through the print zone during the printing process. Such systems can include motors, gears, rollers, sensors, and other components that work in conjunction to move the media incrementally. During each incremental movement of the media, a printing element, such as a print head, causes text and/or images to be applied to the media in rows or swaths.
However, manufacturing tolerances, assembly variations, and other imperfections in such indexing components can cause discrepancies between the desired or expected position of the media and the actual position which is realized. For example, one typical component in a media indexing system is a feedroll or feedroller which contacts the media and forces the media through the printing device. Manufacturing tolerances can cause the feedroller diameter to deviate from its ideal diameter and can also cause the feedroller circumference to deviate from its ideal circular shape. The deviation of the actual feedroller diameter from the ideal feedroller diameter can produce a cumulative feedrate error which corresponds to the average deviation in the desired media position during the movement. For example if the diameter is smaller than ideal, xe2x80x9crunoutxe2x80x9d (feedrate) errors will occur causing the media to be underfed. In addition, a deviation of the actual feedroller shape from the ideal circular shape and/or a deviation of the axis of rotation from center, can produce irregular rotation and a substantially sinusoidal xe2x80x9conce-per-revolutionxe2x80x9d (eccentricity) errors in the indexing of the media.
Other similar deviations in other indexing components can also introduce such errors in the indexing of the print receiving media. For example, eccentricity in the encoder wheel used to sense the feedroller position as well as various forces on the media being moved can cause the media to be advanced too little or too much. Such errors can vary within a printing device based upon the media type, environmental factors (such as temperature and humidity), and mechanism wear.
These media positioning errors can result in an undesirable appearance of the printed image. For example, indexing the media too far (i.e., overfeeding the media) might result in a gap or blank band between print swaths, while indexing the media too little (i.e., underfeeding the media) might result in overlapping print swaths that could create dark horizontal bands in the resulting image. Such swath misplacements can be particularly noticeable during particular printing modes or resolutions.
To compensate for such errors, media indexing calibration and compensation control systems and methods can be utilized. Such systems and methods can measure the system error and provide corresponding compensation to media indexing system components, to attempt to increase media positioning accuracy.
However, some media indexing compensation methods can require expensive components and control electronics, and therefore may only be suitable for use with expensive printing devices. Still other media indexing compensation techniques can require complicated and time-consuming continuous control routines, can be error prone, and cannot operate correctly if errors in the system develop.
Accordingly, it is desirable to provide improved media indexing error compensation methods and systems. In addition, it is desirable to provide improved systems and techniques for media indexing error compensation that increase media indexing accuracy with greater efficiency and without high cost. Moreover, it is desirable to provide improved indexing error compensation methods and systems that can accommodate error conditions.
Accordingly, it is an advantage of at least one embodiment of the invention to provide improved accuracy of media indexing with efficiency and without high cost.
In one embodiment, a method for accurately indexing print receiving media is provided comprising identifying a desired amount by which the print receiving medium should be indexed in order to print at the next location for the image being printed, determining an ideal indexing command for causing the indexing system to index by the desired amount, and adjusting the ideal indexing command based upon a compensation factor in order to compensate for imperfections in the indexing system. The ideal indexing command is adjusted only once per indexing of the print receiving medium by the desired amount. The method further comprises utilizing the adjusted ideal indexing command to move the moveable component and to index the receiving medium by the desired amount in order to print at the next location for the image being printed.
According to another embodiment, a method for accurately indexing print receiving media is provided utilizing executable instructions. The method comprises identifying a desired amount by which a print receiving medium should be indexed, and determining an indexing command for causing media indexing system to index the media by the desired amount. The method further comprises determining whether a sensor for identifying a home position is operational, and if the home position sensor is operational, applying compensation to the indexing command to calculate a final indexing command. If the h sensor is not operational, the method utilizes the indexing command as a final indexing command, which is then used for controlling the indexing system to index the media by the desired amount.
In another embodiment, a method for accurately indexing print receiving media on a printing device is provided, the method comprising providing a media indexing system comprising a moveable component capable of indexing a print receiving medium in response to an indexing operation. The media indexing system further comprises an encoder in communication with the component and a counter. The method also comprises identifying a desired amount by which the print receiving medium should be indexed, determining an indexing command based upon the desired amount, utilizing the indexing command to cause the component to move and to index the medium, and incrementing the counter during the movement of the component according to the corresponding rotation of the encoder. In addition, the method comprises periodically locating a home position on the encoder and identifying the value of the counter when the home position on the encoder is located, and conducting a reset operation if the value of the counter deviates from an expected value by a predetermined amount.